With the rapid development of Internet technologies, various online services have been provided to users via the Internet, such as online transactions, online gaming, social networking, etc. Because of vulnerabilities in networks, security has become a critical issue for online services. Some known online service providers use verification codes to authenticate users. Typically, a user provides a cell phone number in requesting an online service at a terminal device. A user-authentication server sends a text message including a verification code to the user's cell phone. After receiving the verification code at the cell phone, the user then uses that verification code to complete a user authentication process at the terminal device, such that the online service can be provided to the user at the terminal device. Such a user authentication method, however, is not effective if the text message cannot be delivered to the user's cell phone in a timely manner (e.g., due to a network anomaly, a cell phone malfunction, a delay caused by a network congestion, etc.).
Therefore, a need exists for a method, device and system that can enable robust user authentication under various network conditions.